Reference — Fundamentals
Lung Volumes & Capacities
A reference to the four lung volumes and four capacities — tidal volume, IRV, ERV, and RV, and the IC, FRC, VC, and TLC they combine into — with typical adult values and what each one means clinically. The volumes are the non-overlapping building blocks; the capacities are simply sums of two or more of them.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Lung volumes are the four non-overlapping compartments of gas in the lungs; capacities are sums of two or more volumes. Simple spirometry measures the volumes a patient can move at the mouth, but residual volume — and any capacity that contains it (FRC and TLC) — cannot be measured by spirometry and requires body plethysmography, helium dilution, or nitrogen washout.
The Four Lung Volumes
| Volume | Abbrev | Typical Adult Value | Definition |
|---|---|---|---|
| Tidal Volume | VT | ~500 mL (about 6 – 8 mL/kg) | Air moved in a normal quiet breath. |
| Inspiratory Reserve Volume | IRV | ~3000 mL | Extra volume inhaled beyond a tidal breath. |
| Expiratory Reserve Volume | ERV | ~1100 mL | Extra volume exhaled beyond a tidal breath. |
| Residual Volume | RV | ~1200 mL | Gas remaining after a maximal exhalation; cannot be exhaled and is not measured by spirometry. |
Typical adult values scale with height, sex, and age — women run roughly 20 – 25% lower than these reference figures.
The Four Capacities
| Capacity | Abbrev | Composition | Typical Adult Value |
|---|---|---|---|
| Inspiratory Capacity | IC | VT + IRV | ~3500 mL |
| Functional Residual Capacity | FRC | ERV + RV | ~2300 mL |
| Vital Capacity | VC | IRV + VT + ERV | ~4600 mL |
| Total Lung Capacity | TLC | All four volumes | ~5800 mL |
- IC — The most air inhaled from a resting end-expiratory point.
- FRC — The gas remaining after a normal exhalation; the resting equilibrium between lung recoil and chest-wall spring.
- VC — The most air exhaled after a maximal inhalation.
- TLC — The total gas in the lungs after a maximal inhalation.
Clinical Notes
- Obstructive disease (COPD, asthma). Air trapping raises RV, FRC, and TLC and reduces VC; the FEV₁/FVC ratio is under 0.70.
- Restrictive disease (fibrosis, edema, chest-wall and neuromuscular disorders). All volumes fall, TLC is reduced, and the FEV₁/FVC ratio is normal or increased.
- Some volumes cannot be spirometered. RV, FRC, and TLC cannot be measured by spirometry — they require body plethysmography, helium dilution, or nitrogen washout.
- FRC is where PEEP does its work. PEEP raises end-expiratory lung volume to hold recruited alveoli open.
- Interpret against predicted, not absolutes. Predicted values depend on height, sex, age, and ethnicity, so interpret a patient’s numbers against their own predicted set.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Pulmonary function testing and lung volumes chapters.
- Wanger J, Clausen JL, Coates A, et al. Standardisation of the measurement of lung volumes. Eur Respir J. 2005;26(3):511-522.